externals directory. This is in particular useful because though
most systems have bzip2/bunzip2, they don't always have libbz2,
which we need for bsdiff/bspatch.
it automatically removes log files when they are no longer needed.
*** IMPORTANT ***
If you have an existing Nix installation, you must checkpoint the
Nix database to prevent recent transactions from being undone. Do
the following:
- optional: make a backup of $prefix/var/nix/db.
- run `db_checkpoint' from Berkeley DB 4.1:
$ db_checkpoint -h $prefix/var/nix/db -1
- optional (?): run `db_recover' from Berkeley DB 4.1:
$ db_recover -h $prefix/var/nix/db
- remove $prefix/var/nix/db/log* and $prefix/var/nix/db/__db*
log on commit. This means that there is a small change that some
transactions may be rolled back in case of a system crash, but this
should not be a problem (it merely might cause some expression
realisations to be rolled back), and it vastly improves performance.
* Upgraded to ATerm 2.0.5 (which also includes Armijn's 64-bit
patches).